1. Field of the Invention
The present invention relates to pulse combustion devices using flapper-type gas and air inlet valves, and more particularly to an improvement of a flapper-type air inlet valve assembly in the pulse combustion device.
2. Description of the Prior Art
In a conventional pulse combustion device of this kind, flapper-type gas and air inlet valves are adapted to supply gaseous fuel and air into a combustion chamber, and a tailpipe is connected to the combustion chamber to take place therein resonant combustion of the mixture of gaseous fuel and air and to exhaust therefrom the combustion products. In FIGS. 3 and 4 there is illustrated such a conventional pulse combustion device as described above which comprises a cylindrical support member 12 forming therein a mixing chamber 16, a valve housing assembly 20 coupled with the support member 12, a flapper-type gas inlet valve 50 disposed within a cylindrical member 21 of housing assembly 20, and a flapper-type air inlet valve unit mounted on an annular flange member 25 of housing assembly 20. The cylindrical member 21 forms therein a gas passage 22 in open communication with the mixing chamber 16, and the flange member 25 forms therein an annular space 26a and is formed with a plurality of circumferentially equi-spaced openings 26b. The annular space 26a and openings 26b are arranged to form a plurality of circumferentially equi-spaced air flow passages 26 in surrounding relationship with the gas passage 22. The air inlet valve unit includes an annular valve plate 1 secured to the cylindrical member 21 and flange member 25, an annular perforated backer plate 3 fixed to the valve plate 1 through annular spacers 5, and an annular air flapper 4 movable between the valve plate 1 and backer plate 3. As shown clearly in FIG. 4, the valve plate 1 is formed with a plurality of circumferentially equi-spaced radial slots 2 for allowing the flow of air passing therethrough from the air flow passages 26 into the mixing chamber 16.
During operation of the pulse combustion device, the air flapper 4 reciprocates in a limited space between the valve plate 1 and backer plate 3 to open and close the radial slots 2 in valve plate 1 at a frequency of pulse combustion. In general, it is desirable that the movement spacing of the air flapper 4 is ranged from about 1.2 mm to 1.6 mm to effect stable combustion of the mixture. If the movement spacing of the air flapper 4 was more than 1.6 mm, smooth reciprocation of the air flapper 4 would not be effected, resulting in unstable combustion of the mixture and in damage of the air flapper in a short period of time. For this reason, a supply amount of air is limited by the size of the air flapper 4. Meanwhile, if the air flapper was enlarged in size to increase combustion capacity of the device, smooth reciprocation of the air flapper would not be effected, resulting in unstable combustion of the mixture. For this reason, it was difficult to increase combustion capacity of the device.